Brick fireplaces have been conventionally built entirely from brick with a clay flue liner. Brick has been used to form the firebox and the throat of the fireplace. The throat, or smoke chamber as it is sometimes known, tapers inwardly and upwardly from the firebox to the relatively small tubular clay flue liner extending through the chimney.
Fireplaces come in all sizes but the cross-sectional dimensions of the firebox is always larger than those dimensions of the flue of a fireplace One function of the throat in a fire-place is to gradually reduce the cross-sectional dimensions of the area between the firebox and the flue of a fireplace.
A conventional fireplace may have, for example, a brick firebox measuring 29 inches (73.7 cm) wide by 20 inches (50.8 cm) deep and a clay flue liner measuring 9 inches (22.9 cm) deep and 13 inches (33 cm) wide. The brick throat provides a transition between these two sets of dimensions. The prior art process of making the throat from brick requires a lot of brick to fill in the space between the firebox and the relatively small flue. Installation of the brick is time consuming to the point that the making of a brick throat accounts for a significant amount of the overall cost of a brick fireplace.
The cost of a conventional brick fireplace has been instrumental in the development of what are known as prefabricated fireplaces. Prefabricated fireplaces are less expensive than conventional brick fireplaces because they are usually smaller and because they use less expensive materials which are not as rugged and long lasting as brick. The firebox and throat of a prefabricated fireplace are typically made from a frangible refractory lining.
The economy of lining the fireplace throat with selected pieces of clay flue liner instead of an otherwise all-brick fireplace reduces the cost of brick fireplaces to be competitive with prefabricated fireplaces while retaining the advantageous efficiency and durability of the all-brick fireplace.